1. Field of the Invention
The present invention relates to a processing method for radar signal with dual pulse repetition frequency, and more particularly, to a method applying in driving radar sensor for obtaining Doppler shift by emitting different signals with different pulse repetition frequencies to performing detections and obtaining relationships between the different repetition frequencies and associated echo signals
2. Description of the Related Art
A radar speedometer uses the Doppler Effect generated when transmitting electromagnetic wave to perform the velocity measurement. When distance between the object measured and the radar gets shorten, the echo frequencies received by the radar increased; otherwise, when the object moves away from the radar, the echo frequencies received by the radar decrease. Thereby, information of the object measured is obtained according to the frequency variation, for example, distance, relatively velocity, etc.
The FMCW (frequency-modulated continuous wave) radar is one of widely used radars, the advantages of the FMCW radar includes: the measurement result can be more accurate, the echo wave received and transmission signal not overlap each other in the time domain so as to perform the receiving and transmission operation via a single antenna to simplify size of the structure.
However, signals of the FMCW radar can be processed by using 2D (Two Dimension) fast Fourier transform (FFT) so the object measured and the ground clutter can be effectively separated and also perform coherent integration process to increase the radar coverage. The repetition frequency (PRF) of the FMCW radar generally is 1 KHz because of TR-PLL and DSP-MCU. From the Doppler shift, the associated unambiguous velocity of fd is 6.2 m/s (22.3 km/h) which does not confirm to the detection of the general vehicle speed when the radar transmission signal wavelength is 0.0124 m. If want to increase the detection limit to achieve the unambiguous velocity over 27.778 m/s (100 km/h), the associated Doppler shift is fd˜4.46 KHz, and the repetition frequency of radar pulse must be 4.46 KHz or more for avoiding the inaccurate detection result. Therefore, it is difficult to increase the detection limit based on the TR-PLL and DSP-MSU.
For the reason that the conventional method and device could not effectively solve the problem of increasing the detection limit, a need has arisen to propose a novel processing method for radar signal with dual pulse repetition frequency in order to overcome the aforementioned problems.